1. Field of the Invention
This invention relates to apparatus and a method for compressing unprocessed phase history synthetic aperture radar (SAR) digital data information for transmission by wide band data links and for decompressing the transmitted compressed digital information. More specifically, the present invention relates to a new method and hardware apparatus for compressing unfocused phase history SAR data which was heretofore incompressible for reasons to be discussed hereinafter.
2. Description of the Prior Art
Unprocessed SAR data has been transmitted to ground stations where the data is processed into enhanced images. It has been suggested that the bandwidth of the transmitted signal could be reduced by compressing the data to be transmitted to the ground station. However, if prior art data compression techniques were employed it would be necessary to convert the unfocused SAR phase history data into processed focus phase history data in order to compress the data by conventional transform techniques.
The digital data output from conventional SAR devices produces unfocused compressed phase history data which heretofore has ben incapable of being compressed by conventional transform techniques. If special fast fourier transform (FFT) techniques were employed to focus the unfocused phase history data at the airborne station, heavy complex equipment would be required. The weight of the FFT processing apparatus and the conventional transform data compression apparatus presently employed in ground stations is so large and so heavy that it cannot be presently incorporated into aircraft or satellite stations.
It would be extremely desirable to provide a simple and lightweight circuit apparatus and method which would permit direct data compression of SAR digital unfocused phase history pixel data.